Silver halide color photographic elements comprise one or more light sensitive layers coated on a support. Typically the support is a sheet of a transparent or translucent film, commonly referred to as a film base. Common film base materials for photographic elements are cellulose triacetate and poly(ethylene terephthalate). These materials have properties which render them suitable for photographic applications. More recently it has been proposed to use poly(ethylene napthalate) as a film base for photographic elements which are intended to be used in a cartridge of reduced diameter which requires rolling the film more tightly than previously. While conventional 35 mm film spools have diameters of about 11 mm, spools for proposed film cartridges have diameters as low as 7 mm, or lower. This is discussed in U.S. Pat. Nos. 5,294,473 and 5,368,997, incorporated by reference herein, which suggest that poly(ethylene naphthalate) has higher stiffness and lower propensity to take up core-set than either cellulose triacetate or poly(ethylene terephthalate).
Two disadvantages of poly(ethylene naphthalate) as a film support are as follows. In order to realize the curl and core-set advantages of films made from poly(ethylene naphthalate), it is necessary to anneal the film at elevated temperatures for substantial periods of time. Even then, the core-set and curl characteristics are not as good as would be desired. Secondly, the higher glass-transition temperature, or Tg, of poly(ethylene naphthalate) results in a higher melt viscosity and greater difficulty in melt processing.
Accordingly, it would be desirable to provide a film base with improved physical properties and processability. In particular it would be desirable to have a film base that has a lower propensity to curl and take up core-set while retaining adequate stiffness and tear strength. It also would be desirable to have such a film base which can be annealed using milder conditions. It also would be desirable to have such a film base that has a lower Tg and better melt processability.
We have found that a novel blend of a polyester containing at least 30 weight percent cyclohexylene dimethanol and a polycarbonate containing bisphenols provides a film base with a number of useful properties which makes it particularly advantageous for photographic films.